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A highly sensitive nanometer-scale carbon monoxide sensor that uses an innovative fabrication technique is now in development, researchers said.

Carbon monoxide (CO) can have adverse effects on the health of people exposed to it, so it becomes necessary to have good, low-cost carbon-monoxide sensors available, said researchers at the Indian Institute of Science.

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Typically, a sensor would be a thin, current carrying plate whose resistance changes on exposure to carbon monoxide. This in turn changes the value of the current flowing through it. This change when measured indicates the level of carbon monoxide in the air.

Most sensors available today are in the micrometer range, a nanometer-sized detector would have a higher sensitivity, but the cost of manufacturing it goes up as the size decreases.

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This is where C.S. Prajapati and his team at the Indian Institute of Science comes in.

To build this zinc-oxide (ZnO) nanostructure on a silicon wafer substrate, the researchers first placed tiny polystyrene beads on the wafer. These beads arrange themselves into a hexagonal close-packed structure on the oxidized silicon wafer.

Maintaining a reasonable level of vacuum, a high voltage is applied which “etches away” the surfaces of the beads until a gap of desired thickness is formed between adjacent beads. Then zinc oxide is deposited on the system. 

This occupies the spaces between the beads, forming a honeycomb like nano-mesh that can function as a nanosenor. 

“Scaling down from 10 micrometer feature size to 10 nanometer feature can enhance the efficiency 1,000 times. However, the development cost of nanostructured gas sensors using existing lithography tools is really very high, which eventually impacts the overall cost of the device,” said Navakanta Bhat, chair and professor at the Centre for Nano Science and Engineering, Indian Institute of Science, and an author of the paper.

This device is also easy to scale for mass production.

“Nanostructure-based gas sensors are very promising in their performance due their high surface-to-volume ratio. The existing techniques to create honeycomb nanostructures using photolithography and e-beam lithography are expensive and time-consuming. The proposed technique can potentially reduce the cost by more than 50 percent,” Bhat said.

“The Ministry of Electronics and Information Technology has a vision of deploying such sensors in large scale for pollution monitoring in large cities like Delhi and Bengaluru. For instance, if the sensors are installed in all traffic intersections, we can do real time mapping of pollution hot-spots in a city. This would be an enabler in realizing smart cities,” Bhat said.

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